<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .main{
            width: 500px;
            height: 500px;
            border: 1px solid #000;
            background-color: skyblue;
            display: flex;
            flex-flow: row wrap;
            align-content: center;
        }

        .box{
            width: 100px;
            height: 100px;
            background-color: red;
        }
        .box:nth-child(4){
            height:50px;
            background-color: blue;
            align-self: flex-end;
        }


    </style>
</head>
<body>
<div class="main">
    <div class="box">1</div>
    <div class="box">2</div>
    <div class="box">3</div>
    <div class="box">4</div>
</div>
</body>
</html>
